A study in India that failed to detect drug resistant tuberculosis in over a third of samples has raised questions about the reliability of a molecular diagnostic test for the disease endorsed by the World Health Organization more than three years ago.

In the study of patients from Punjab the Xpert test, which was designed to simultaneously diagnose tuberculosis and detect resistance to rifampicin—a key first line drug for the infection—falsely classified 21 of 59 samples (35.5%) as susceptible to rifampicin.1

Doctors at the All India Institute of Medical Sciences in New Delhi, who conducted the study, said their findings showed that the test might not detect certain genetic mutations that could be associated with drug resistant tuberculosis.

Sarman Singh, professor of clinical microbiology at the institute who led the study, told The BMJ, “These are disturbingly high false negative …